Rotary wing aircraft utilize propulsion systems to power aircraft flight. These propulsion systems convert stored energy into mechanical work to drive one or more rotor systems for flight. Energy (typically stored in chemical form as fuel) is supplied to an energy conversion device (typically a plurality of internal combustion engines such as a turbine engine, spark ignition engine, or compression ignition engine), which converts the energy into mechanical work. A drive system transmits mechanical work through a plurality of transmission mechanisms (e.g., main rotor gearbox(es), a tail rotor gearbox, intermediate gearbox(es), drive shafts, drive couplings, etc.) to drive the rotary wing aircraft's thrust generating rotors.
In an emergency, e.g., in the event of an engine failure of a multi-engine aircraft, the aircraft must rely on contingency power from the remaining operating engine(s) for a predetermined duration so as to place the aircraft in a safe flight regime and react to the engine failure. Emergency power for an example turbine engine is typically defined as One Engine Inoperative (“OEI”) ratings with varying limits and durations. When operating to OEI limits, the turbine engine is run at increased speeds and/or temperatures during an emergency for typical durations of 30 seconds to 2.5 minutes in order to provide a limited duration increased power to achieve a safe flight condition. However, increases to these time limited emergency power ratings is difficult, expensive, and may not be possible over the entire envelope without significant engine redesign.